Acoustic baffle construction



Oct. 29, 1957 W. T. HARRIS ACOUSTIC BAFFLE CONSTRUCTION Filed April 28, 1954 FIG. 4.

FIG.

1m 50/? .r M45675 BY 1 T 11W 764%? ATTO R N EY5 2,811,216 Patented Oct. 29, 1957 anna s ACOUSTIC, eo ssrhhcuqs Wilbur T. Harris, southhury gojnn, assignorto The Harr Thahsfl s r rrhratipni mdhu y, 20m, a rpo a on Chhh hfih t Application April 28, 1954, Serial No, 426,219 .lf -Claim e (Cl: 1&1

My invention relates to an acoustic-'baflie eonstruotion, as of the sort which may be employed in underwater-sound transducer installations where' it is. necessary to shield a transducer from directi l no se hriaihhtih' ou s d t e transducer or to reflect sound originating from a particular direction.

It is an object of the invention to provide an improved bafiieconstructionn It 'is another object to: provide abafile construction lending itself to flexibly adapted use, depending upon a multitude of installation requirements.

It is a further object to provide an .etnfcient sound-absorbing or re flecting battle for prolonged'underwater use and not susceptible to time-deterioration as oceasioned by water absorption with prolonged underwater exposure.

Other j t a a u h ther featu es Qt no el a invention will be pointed out or wiii "become apparent to those skilled in the art from a reading of the following specification in conjunction with the following drawings. In said drawings, which show, for illustrative purposes only, preferred forms of the invention Fig. 1 is a partly broken, vertical sectional viewof a bafi le construction embodying featuresof the invention;

' 2 is a p rs e-v ew 0. a edu ed sha e v h the sound-absorbent or reflecting face of the baflle of F g, 1; and

s. 3 an 4 a e ra m nta se t on l view i lu modifications.

Briefly stated, the invention contemplates means for li nat 9f t e time-dete io at o fa tor which ha previously hara terize the meat .s9 t ;1=ah en o r h t hs mat r als, such as ai -fill d ub in d rw te hhd ha c Fo lar e-a e ha fiee t has be me tomary to bond rubber or rubber-like material to the exposed surface of the body of sound-absorbent or reflecting material, but, unless excessive thicknesses of such material are applied, the time-deterioration factor (occasioned by slow diffusion of any air from the body into the surrounding water medium) substantially impairs performance. I have discovered that the time-deterioration factor can be eliminated without employing excessive thicknesses of rubber or rubber -like material, and for this purpose I show acoustically transparent metal membranes bonded continuously over the exposed baffle surface and sealed by impermeable means over the continuous peripheral extent of the membrane and of the body.

Referring to Figs. 1 and 2 of the drawings, my invention is shown in application to a baflle contained within a rigid frame 10, defining a central opening for containing the absorbent or reflecting body 11 of the bafile. The body 11 may be of any desired material having a pC characteristic substantially lower than the acoustic impedance of water.

I have indicated by sectioning that body 11 may be airfilled rubber or the like to provide substantially a planar pneumatic compliance, or that it may be loaded with metal flake, mica flake, or other relatively dense particles to provide absorptive or resistive properties. The ruggedness of the assembly may be improved by employment of a rigid backing plate 12 of impermeable material, such as, sheet me a ure b b lt .Qr rive 1 h b We t the rame 0- I P e er th t d 1 hal he PFR Y bonded to the plate 12 with peripherally continuous lateral clearance, as at 14, between the body and the inner wall 15 of the opening. 7

To seal the other side of the baffle, I employ acoustically transparent impermeable means, and have found that a thin memhrane 1 6 of metal, such as aluminum, copper,

stainless steel, orthe like, will serve the purpose. The membrane 16 is preferably bonded securely to the body of compliant or resistive material 11, and the lateral edges 18 of the membrane 16 preferably project peripherally and continuously away from the lateral confines of the body 11. For protection against rupture of the membrane 16 through mishandling, 1' indicate at 19 my preference for a suitably thick layer of acoustically transparent material, such as rubber or neoprene, intimately bonded to the outer surface of the membrane 16 and preferably co: extensive therewith.

In order to seal the lateral edges of the baffle, I so form th la al ch hcs hi th me an 6 t edges 1 project short of the inner wall 15 of the frame and so that edges 18 are offset substantially axially (or transversely) in from the outer face or limit 26 of the frame. The edges 18, however, should also be axially spaced from the other limit of theframe, as defined by the back plate 12. Sealing may then be effected by potting substantially all the remaining space14, 2 1in the opening of the frame and thus continuously and peripherally overlapping the seal membrane 16, the body 11, and the otherwise-exposed interfit of the body 11 with the backing plate 12. The potting may suitably be any of the well-known acous: tically transparent impermeable plastics, such as 3 P013: n erized epoxy eomposition. i

In Fig. 3, I show a modification in which the body 31) of acoustically resistive or compliant material is sealed on both faces by a symmetrical employment of thin, flexible, acoustically transparent membranes 3132. The mem: branes 3132 and bonded sheathing 33 may be of the construction described at 16-19 in Fig. 1. Thus, periph: erally projecting membrane edges 34 may be axially spaced from each other and from the axially outer limits 35-36 of frame means 37. A potting 3,8 of impermeable sealing material may complete the assembly and may overlap all exposed projections and interfits between membranes 31-:32, body 30, and sheaths 33. To enhance the axial support afiorded by frame means 37, I show the frame to be of channel-shaped section, with a channel groove defined by spaced walls -41 extending inwardly, that is, toward the body 30, and peripherally overlapping the outward projection of limits 34 of the impermeable membranes.

In Fig. 4, I show a modification in which resistive and compliant'properties are embodied in a construction similar to Fig. 1 but through employment of separate layers -51 of resistive and compliant materials. The resistive layer 50 may be pellet-filled rubber or the like, and the compliant layer 51 may be air-cell rubber. Otherwise, the construction may be the same as in Fig. 1, and corresponding reference characters are therefore employed.

It will be seen that I have described an improved baflie construction featuring complete impermeable sealing of acoustically compliant or resistive materials, so as to assure no loss of these properties by reason of air or water seepage during prolonged underwater exposure. This feature is achieved without employment of excessively bulky sheathing. The construction is rugged and lends itself to adaptation to meet a wide variety of specific installation requirements. In the employment of air-filled or gas-filled materials for bodies '1130, my constructions provide nearly perfect reflectors for sound from either direction,

except at frequencies below which they become acoustically transparent; they are essentially low-pass filters, with the cut-off frequency depth-dependent but not timedependent.

While I have described the invention in detail for the preferred forms shown, it will be understood that modifications may be made within the scope of the invention as defined in the claims which follow.

I claim:

1. A baflle comprising a rigid frame having an opening therein and defining a baffle area in said opening, a body of acoustic material within said opening and spaced from the inner edges of said frame, said acoustic material having an impedance lower than that of water, impermeable sheaths on both sides of said body, one of said sheaths being acoustically substantially transparent, and a potting of impermeable sealing material overlapping the edges of said transparent sheath and of said body and filling the space between said body and said frame and said other sheath.

2. A baffle comprising a relatively stilf backing plate, a body of acoustic material supported on one sideof said plate and of lesser extent than said plate whereby peripheral parts of said plate project outwardly of said body, an acoustically transparent impermeable sheath over the exposed side of said body and projecting peripherally over the lateral limits of said 'body, and impermeable sealing means in intimate sealing relation with said body and with peripherally projecting parts of said plate and said sheath.

3. A batlle according to claim 2, in which said sheath comprises a thin flexible metal sheet.

4. A baffle according to claim 2, in which said sheath comprises an outer layer of rubber-like material and an inner impermeable membrane.

5. A bafiie according to claim 2, in which the impedance of said material includes a substantial compliance component.

6. A bafile according to claim 2, in which the impedance of said material includes a substantial resistance component.

7. In a bafile, a body of acoustic material, two thin metal flexible membranes bonded to opposite sides of said material and projecting peripherally of the lateral confines of said body, rigid means peripherally framing said body and membranes, and impermeable sealing material overlapping the peripherally projecting ends of said membranes and filling the space therebetween and bonded to said rigid means.

8. A baflie comprising an open frame of channel-shaped section with a channel groove facing inwardly, a body of acoustic material in the Opening of said frame, two impermeable flexible sheaths intimately contacting opposite sides of said body and projecting peripherally of the lateral confines of said body, said peripheral projections extending into the channel groove, and a filling of impermeable plastic sealing material filling the channel and peripherally sealing the projecting edges of said membranes and the exposed lateral edges of said body.

9. A baflle comprising a body with a layer of compliant material and a layer of resistive material, means sheathing both sides of said body, said means including acoustically transparent impermeable means on one side of said body, and an impermeable plastic filler overlapping the lateral edges of said impermeable means and covering the lateral edges of said body.

10. A bafile comprising a rigid frame having an opening therein and defining a baflle area in said opening, a resistive and compliant body in said opening and spaced from the inner edges of said frame, impermeable sheaths on both sides of said body, one of said sheaths being acoustically substantially transparent, and a potting of impermeable sealing material overlapping the edges of said transparent sheath and of said body and filling the space between said body and said frame and said other sheath.

11. A baflle according to claim 10, in which said other sheath is a sheet of metal anchored peripherally to said frame.

12. A baffie according to claim 10, in which said body comprises separate resistive and compliant layers.

, 13. A baflle comprising a relatively stifr metal sheet, a body of acoustic-impedance material having an impedance lower than that of water and overlying one side of said sheet, an impermeable flexible metal sheath over the exposed side of said body, and a peripheral seal of impermeable sealing material overlapping the edges of said sheath and of said body and sealed to said sheet.

14. A baifle comprising a body of acoustic-impedance material, acoustically transparent impermeable means sheathing both sides of said body, and an impermeable plastic filler overlapping the lateral edges of said impermeable means and covering the lateral edges of said body. 1

References Cited in the file of this patent UNITED STATES PATENTS 1,378,420 Merritt May 17, 1921 2,131,762 Smith Oct. 4, 1938 2,169,370 Parkinson Aug. 15, 1939 2,496,060 Mell et al. Jan. 31, 1950 

